The shape of the border to draw around the decoration's container.
The decoration's container is the area which is filled if filled is true and bordered per the border. It's the area adjacent to InputDecoration.icon and above the widgets that contain InputDecoration.helperText, InputDecoration.errorText, and InputDecoration.counterText.
The border's bounds, i.e. the value of
the area to be filled.
This property is only used when the appropriate one of errorBorder, focusedBorder, focusedErrorBorder, disabledBorder, or enabledBorder is not specified. This border's InputBorder.borderSide property is configured by the InputDecorator, depending on the values of InputDecoration.errorText, InputDecoration.enabled, InputDecorator.isFocused and the current Theme.
final InputBorder border